1. Field
The current disclosure relates to cavity-resonator filters, and more specifically, but not exclusively, to cavity-resonator filters with pedestal-based dielectric resonators.
2. Description of the Related Art
Conventional dielectric-loaded cavity resonators are devices that include one dielectric posts inside one metallic chamber, while conventional dielectric-loaded cavity filters are devices that include one or more dielectric-loaded resonators interconnected in metallic chambers. Dielectric-loaded cavity resonators are used as radio-frequency (RF) filters thanks to their high Q factors. The Q, or quality, factor is a parameter that indicates a resonator's level of under-damping, where a higher Q factor indicates that resonant oscillations in the resonator die out more slowly.
Conventional dielectric-loaded cavity resonators use cylindrical dielectric posts. Individual dielectric-loaded resonators may couple to other dielectric-loaded resonators by capacitive coupling or inductive coupling. Couplings between resonators of a filter correspond to zeros and poles in the frequency-response characteristics of the filter. The numbers of poles in the frequency-response characteristics of a resonant filter may be increased by increasing the number of resonators. The number of zeros in the frequency-response characteristics of a resonant filter may be increased by increasing the number of cross coupled dielectric-loaded resonators as opposed to serial coupled resonators. Generally, the greater the number of zeros and poles in the frequency-response characteristics, the more flexibly the frequency-response curve can be shaped. More zeros can help define a sharper drop-off from the pass-band and, consequently, provide a higher Q factor.
Capacitive coupling between dielectric-loaded resonators is conventionally accomplished using a conductor between the coupled posts. Inductive coupling is conventionally accomplished using openings between the chambers of the coupled resonators. These openings are sometimes referred to as irises.
FIG. 1 shows a perspective view of an uncovered conventional resonator filter 100. The top side (not shown) of the filter 100 is a rectangular metal plate that covers the shown uncovered portion. Filter 100 comprises metal housing 101, which houses four dielectric resonator posts 102(1), 102(2), 102(3), and 102(4) arranged within a 2×2 array of corresponding resonant cavities 103(1), 103(2), 103(3), and 103(4). Filter 100 includes source port 105(1) and load port 105(2), which connect to input and output, respectively, of filter 100. Ports 105 are in the form of apertures in conductive micro-strips.
Some of the walls separating adjoining resonant cavities have openings between them, such as opening 104(1) between cavities 103(1) and 103(2). As noted above, opening 104(1) between cavities 103(1) and 103(2) allows for inductive coupling between the corresponding dielectric resonators 102(1) and 102(2).
Capacitive coupling between pairs of dielectric resonators may be accomplished using coupling conductive wires, such as conductor 106 between dielectric resonators 102(1) and 102(4). Note that coupling conductor 106 comes close to, but does not contact, dielectric resonators 102(1) and 102(4). The incorporation of conductor 106 into filter 100 increases the costs of production for filter 100 and restricts the filter topology such that length of 106 is short.